Use of the Auditory Biofeedback system to improve a patient*s partial weight bearing compliance: a feasibility study

After some types of surgery on the lower extremity of a patient, partial weight
bearing is instructed by the surgeon or physician. During the course of
rehabilitation, usually several weeks, the allowed load is slowly increased
until full weight can be applied. The partial weight bearing on the affected
limb, is achieved by the use of crutches or a walking frame.

The assessment of the applied load on the limb in case of partial weight
bearing is often difficult. The instruction of the allowed load consists of
indicating the allowed static load on the limb using scales. Patients are often
unable to translate this static force when walking.

Several biofeedback devices have been developed to provide the patient with
feedback when overloading their limb. However due to high costs, they are
mainly used in clinical settings. It has been shown that patients are not able
to apply the prescribed PWB after training, when they walk unsupervised without
a biofeedback device.

The Auditory Biofeedback (ABF) device "Parbel" is a cheap and wearable system
for providing biofeedback on PWB on a daily basis. This device uses a load
measuring insole combined with an app for data display and feedback on weight
bearing. The allowed load can be programmed into the device by the physician.
When the allowed load is exceeded a warning signal is sounded. Using the ABF
device, patients will have an indication of allowed load during walking
relative to the applied load. In the present study it will be investigated
whether it is feasible to improve a patient's PWB compliance, when using the
improved ABF device.

A previous version of this device was tested in a study with healthy subjects.
Here it was shown that the ABF system could improve the partial weight bearing
compliance of a patient. However from a study with patients recovering from
anterior cruciate ligament (ACL) reconstruction, it became clear, that the ABF
device should be improved. After surgery patients often land on their forefoot,
without heel contact. Because the previous version of the ABF device, only had
a sensor in the heel, no or less load was measured during walking. Also it was
questioned whether the then used piezo electric sensors are the correct sensors
to measure the ground reaction force. Slow pressure changes will not be
observed and patients often load their limb more slowely than healthy subjects.
Furthermore, when wearing the ABF device patients tried to reach the warning
signal as a reassurance that they were applying sufficient load, because they
were instructed not to apply too little load. Therefore it was suggested to
implement a lower threshold, to warn the patient when too little load is
applied.

Now instead of piezo electric sensors, hall sensors in combination with magnets
with the material D30 in between are used. This sensor can measure slow changes
in loading. Hall sensors are transducers that vary in output voltage in
response to a magnetic field. By applying load on the sensor the distance of
the magnet to the hall sensor changes and so the output voltage of the hall
sensor changes. The output voltage can be coupled to the applied load. Five
distance sensors are placed under the ball of the foot and 2 sensor are placed
under the heel of the foot, one under the lateral side and one under the big
toe, to make sure loading of the foot is measured. Also it will be possible to
set a lower threshold to provide the patient from feedback when too little load
is applied.

The hypothesis is, that using this improved ABF system, the patients quickly
learn to apply the right load during walking with feedback and will not be able
to apply the correct amount of load without feedback from the ABF device.
During the learning curve, the interval of the sounded alarms will decrease
when the ABF device is used. Furthermore it is expected that after training
with the ABF device, the patients will not be able to retain their compliance
to PWB. Compliance to PWB will be beneficial to the rehabilitation process.

Primary Objective:
To determine whether it is feasible to use an ABF device to lower the amount of
incorrect steps. Incorrect steps are the steps exceeding the maximum allowed
load or being below the minimum load.
The specific research question that the study aims to answer is:

- Is it possible to increase partial weight bearing compliance using the
Auditory BioFeedback device?

The present study is conducted in preparation of a future randomized controlled
trial, investigating the ability of an Auditory BioFeedback (ABF) device for
partial weight bearing to reduce rehabilitation time of patients that have
undergone leg surgery.

Secondary Objective:
To determine whether the use of an ABF device is satisfactory for patients.
Specific research questions that the study aims to answer are:

- Is the use of biofeedback technology easy to use for therapists and patients?
- Does the biofeedback signal provide the patient with usable information?
- Is there user acceptance and satisfaction of complying with partial weight
bearing instructions of the device?

First session
Prior to the patients normal physiotherapy session, a normal part of their
rehabilitation process after surgery, subjects will participate in the study.
First their weight will be determined using a scale. With this measurement, and
the percentage allowed maximum load assigned to the patients by their
physician, the maximum allowed force will be determined. This way also the
minimum allowed force will be determined. The amount of loading of the limb to
achieve these forces, is demonstrated to the patient using a scale. The
Auditory BioFeedback (ABF) device will be set to this maximum and minimum force.
At the start of the measurements, subjects will be equipped with the ABF device
and explained how to walk with crutches to achieve partial limb loading. The
crutches will be set on the proper height.
The subjects will be randomly divided into two groups. Subjects assigned to
group one will first walk for five minutes with crutches and the ABF device
turned on, but no feedback will be given to the patient. During this time,
patients will try to apply no more than the maximum allowed load, but more
than the minimum amount of load to the affected limb. The ground reaction force
of walking will be recorded by the ABF device. Patients will not receive
feedback on the forces that are recorded, because the sound on the smartphone
is turned off. After five minutes of walking, the subjects will take a short
break while the sound is turned on on the smartphone, so the ABF device can
provide the patient with feedback. An explanation of the functioning of the ABF
device is given. After this, the patients will again walk with crutches for
five minutes while forces are again recorded by the ABF device. During this
time, they are encouraged to change the load on their limb, when the ABF device
gives a warning indicating too much or too little load is applied.
Subjects assigned to the second group (the control group) will participate in
the same measurements but without feedback from the ABF device. The group will
walk two times for 5 minutes as well, with breaks in between, but no feedback
will be provided.

Second session:
Prior to the patients following normal physiotherapy session will participate
in the second session of this research. The allowed force is again determined
using the previous weight measurement and the current maximum and minimum
percentage load assigned to the patient by their physician. The amount of
loading of the limb to achieve these forces, is demonstrated to the patient
using a scale. The Auditory BioFeedback device will also be setup to these
forces.
The patients assigned to the first group will first walk for five minutes with
the ABF device, without feedback and after a short break they will walk for
five minutes with feedback from the ABF device. The patients assigned to the
control group will walk two times with a short break in between with no
feedback given by the ABF device. As in the first session, measurements of the
forces while walking will be recorded by the ABF system and patients do not
receive feedback on these measurements.
After the two five minute walking tests, a short interview will be conducted
with the subjects of both groups. In this interview, subjects from the first
group will be asked about their experience with the ABF device and asked if
they feel the use of the device made a difference in their partial weight
bearing. The subjects from the control group will be asked whether they think
they were able to comply to the PWB instructions or not, if it was difficult
for them to apply the correct amount of load and if they would be interested to
have feedback during walking.

The subjects will participate in two sessions before normal physiotherapy, part
of the prescribed rehabilitation, is conducted. During these sessions, body
weight will be measured one time. First the subjects will be assigned to two
groups. One group receiving Auditory feedback from the ABF device and one
control group, also wearing the ABF device but not receiving feedback. At the
first session, subjects will walk for ten minutes equipped with an ABF device
and crutches. At the second session, subjects will walk for ten minutes
equipped with an ABF device using crutches as well and a short interview will
be conducted afterwards. To avoid fatigue, subjects will be encouraged to take
breaks as needed throughout the sessions. The risks involved are no greater
than normal walking with crutches. Knowledge will be gained about the
effectiveness of the ABF device to improve a patient's partial weight bearing
compliance. When effective, the ABF device might be the first cheap device,
which can be used outside of clinical settings on a daily basis by the patient.
This would lead to better partial weight bearing of the limb and could be
beneficial for the rehabilitation process of patients. Future patients that are
required to use partial limb loading, can therefore benefit from this research.
If the ABF device is able to improve partial weight bearing, a large scale
Randomized Controlled Trial can give more insight into the effect of partial
weight bearing after surgery. This knowledge will benefit all future patients
in this group.